1. Field of the Invention
The present invention relates to an X-ray generating apparatus that applies an electron beam onto a target to generate X-rays.
2. Description of the Related Art
So far, as an X-ray generation source that generates X-rays with a reduced-focus size, a micro-focus X-ray generating apparatus has been widely used. A general X-ray generating apparatus accelerates thermoelectrons emitted from a heated cathode and causes them to collide with a target to emit X-rays. Since an electron current toward the target spreads, application of an appropriate electric field to Wehnelt suppresses spread of the electron current, to thereby cause the electron current to be focused on the target. Since the electron beam minutely reduced in size needs to be applied onto the target, there is known the micro-focus X-ray generating apparatus that controls focusing of the electron beam by using various means.
For example, the X-ray generating apparatus described in the Patent Document 1 includes an X-ray focusing device using an X-ray reflection mirror in addition to a basic configuration including an X-ray tube, an electron gun, an X-ray target, an electron lens, a stigmator, and an X-ray window, to thereby generate X-rays with the focus of compact size or a focus line.
The X-ray focusing apparatus according to the Patent Document 2 are used in two planes, and includes two sets of beam deflection coils provided between an anode of the electron gun and a focusing lens by an electromagnet, to thereby focus the beam onto the center. Furthermore, the X-ray focusing apparatus has an air-cored quadripole magnet as the stigmator that is provided between the focusing lens and the target and that changes the beam having a circular cross-section into an elongated shape. This quadripole can be rotated about the tube axis, to thereby be capable of adjusting the direction of the line focus, and the beam can be moved on the target surface by controlling currents in the four coils of the quadripole.
A compact-type X-ray tube described in the Patent Document 3 adjusts a focus position in the traveling direction of an electron beam and a focus position on the target through the use of an annular permanent magnet provided outside a small diameter portion in order to focus the electron beam on a minute range portion of the target. However, an adjustment method is performed by moving the permanent magnet along the small diameter portion.
FIG. 11 is a perspective cross-sectional view illustrating a conventional X-ray generating apparatus 300 as described above. The X-ray generating apparatus 300 includes an alignment coil 310, an electromagnetic lens 320, a stigmator 340, a target 350, and an X-ray extraction window 360. FIG. 12 is a perspective view illustrating an incident angle α3 of an electron beam e3 with respect to a target 350 and illustrating a take-off angle β3 of X ray x3. The incident angle α3 is set to be large, approximately 78 degrees, and the conventional X-ray generating apparatus 300 irradiates the target with the electron beam by extension of the cross-section of the electron beam by the stigmator 340 and then the X ray is extracted at the X-ray take-off angle is β3 thereof that is set to be small, approximately, for example, 12 degrees. A range surrounded with a broken line illustrated in FIG. 12 indicates an irradiation range of the electron beam on the target. An X-ray generating apparatus 300 causes the electron beam that is generated by the cathode and has passed through a aperture 305, to be focused by an electromagnetic lens 320 that accounts for a large volume of the apparatus.